Method of and apparatus for selectively operating a cooking apparatus with circulating heated air or water vapor

ABSTRACT

The conversion operation of a cooking apparatus which is initially operated using heated air at approximately 250° C. to an operation using water vapor is made possible in a short period of time and without danger by lowering the temperature to approximately 100° C. in the cooking space wall prior to steam or water vapor operation.

This is a divisional of co-pending application Ser. No. 800,470, filedon Nov. 21, 1985, now U.S. Pat. No. 4,701,334.

FIELD OF THE INVENTION

My present invention relates to a food treatment method and apparatusand, more particularly, to a method of and to an apparatus forselectively operating a cooking apparatus with circulating heated airand water vapor or steam.

BACKGROUND OF THE INVENTION

It is known that a cooking process, i.e., the steaming or boiling orother treatment of foodstuffs to cook them, can be accelerated and mademore uniform by circulating hot air in the cooking space by a blowerthereby cooking the comestible product in a uniform manner. The air isdistributed by corresponding guides or baffles. In such apparatus,instead of hot or heated air, use can also be made of water vapor orsteam.

The steam or steaming operation, however, can also be carried out attemperatures up to approximately 100° C., at least where the interior ofthe oven is to be at ambient pressure.

Accordingly, when switching an apparatus, which is initially operated ata temperature of approximately 250° C. by heated air for the firstdescribed cooking mode, it is generally necessary to allow thetemperature to drop to approximately 100° C., lest too much steam beproduced and excessive pressure build-up occur.

The natural cooling of the cooking space to a temperature of 100° C. forthe steaming, however, takes a rather long time which can detrimentallyaffect the quality of the food which is to be cooked and the efficiencyof the cooking operations.

Although one can open the charging door to aid somewhat in lowering thetemperature, heat energy will then be lost.

OBJECTS OF THE INVENTION

It is accordingly an object of the invention to automatically carry outthe conversion from the heated air operation mode to the steam operationmode in a more rapid manner and without energy losses.

It is also an object of the invention to provide an improved apparatuswith means for automatically and selectively operating with heated airor water vapor.

SUMMARY OF THE INVENTION

These objects are attained in accordance with the invention in thatduring changeover of the operation mode from that employing heated airto that of employing water vapor, a cooking space wall is sprayed withcold water for a period of time sufficient to lower the temperature inthe cooking space to about 100° C.

Advantageously, the back wall of the cooking space is sprayed withwater, and ventilating blower or fan for circulating heated air or watervapor, respectively, is arranged at this back wall.

The invention is also concerned with a cooking apparatus for carryingout the method briefly described above, in which a solenoid valve forcontrolling the supply of cooling water is monitored by a thermostatsensor. The cooling unit or system also includes a conduit or similarmeans for supplying water and a spray nozzle directed towards therespective cooking space wall, for example, the rear wall of the cookingspace.

Advantageously, the cooling system comprised of the thermostat sensor,solenoid valve, and the spray nozzle is first actuated in the controlsequence, and in an automatic manner, with respect to the other elementswhich are operational during the steam or steaming operation mode.

Due to the large surface area of the cooking space wall which is sprayedwith the cold water, a large heat exchange surface is provided. The heatabstracted during vaporization of cold water from the cooking spaceensures that the cooking space temperature is lowered to the required100° C. within a short period of time. The energy used for vaporization,however, is not wasted since the resulting water vapor is used for thesubsequent steam operation mode.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of my inventionwill become more readily apparent from the following description,reference being made to the accompanying highly diagrammatic drawing, inwhich:

FIG. 1 is a vertical cross section through the cooking apparatus;

FIG. 2 is a horizontal cross section through the cooking apparatus; and

FIG. 3 is a circuit diagram for the oven.

SPECIFIC DESCRIPTION

The cooking space muffle 1 is insulated for heat and can be loaded atthe forward end by way of a door 2. The gaseous swirls created in thecooking space 3 are precluded from leaving the apparatus because of adoor seal 4 which is correspondingly arranged thereabout.

Air guide sheets or baffles 5 serve to uniformly distribute the heatingmedium which is circulated by the ventilating wheel blower or fan 6(FIG. 2). The circulating heated air displaced by the blower 6 is passedalong the electrical resistive heating bodies or elements 7 and reaches,via the lateral air guide sheets 5, between and to the individual tiersor levels of the cooking space 3. From here the hot air is againcentrally sucked-in by the blower 6. The motor 14 drives the ventilatingwheel 6.

In the steam operation mode, the steam generator 9 is heated by theheater 8, and water vapor is passed from the steam producer 9 via thesteam conduit 10 to the cooking space.

One may wish to cook initially at 250° C. using heated air, and then toconvert to the steam operation mode by introduction of water vapor; forthis, first the solenoid valve 11 of the cooling system or unit isopened, and cold water passing through conduit 11a is sprayed from anozzle 12 (FIG. 1) onto the rear wall of the cooking space. The valve 11is also referred to as water valve and serves to control the flow ofcooling water.

The cooking space is connected by way of the drain and venting conduit13 with the free atmosphere, and formation of overpressure will beavoided.

A steam thermostat 15a (FIG. 2) is arranged in the sensor duct 15. Thethermostat 15a controls the steam producer 9 during the steam operation.The reference numeral 16 indicates a safety valve atop the steamproducer 9.

The sequence on conversion from heated air operation to steam operationis as follows:

During the control adjustment of the apparatus to heated air operation,the ventilating wheel 6 is driven by the motor 14, and the heatingelements 7 are operational when the desired heated air temperature of,for example, 250° C. has not been attained. As soon as the apparatus isswitched to steam operation, the valve 11 is opened for such a period oftime until the thermostat sensor 17 indicates that a sufficient volumeof cold water has been sprayed onto the rear wall to lower thetemperature in the cooking space to approximately 100° C., Then, watervapor is directed in the usual manner from the steam producer 9 into thecooking space.

The required control steps can be carried out automatically when theoperating person switches the apparatus from heated air operation tosteam operation.

A selector switch 18 has, in addition to its "off" position, a "hot air"position and a "steam" operation.

In its "hot air" position, the switch can not only connect the blowermotor 14 to the electric current source 19, but also energize theheaters 7 for heating the air to the desired hot air temperature ascontrolled by the oven thermostat 20.

In the "steam" position, however, the switch 18 can initially energizethe solenoid valve 11 through the rearwall temperature thermostat 17which, as the :rear wall temperature drops to 100° C., deenergizes thevalve 11, to terminate the cold water spray, and opens the solenoidsteam valve 21 which, like the heater 22 of the steam generator areunder the control of the thermostat 15a mentioned earlier.

Thus, the cooking apparatus can readily be selectively used: initiallyin an operation with heated air of approximately 250° C.; and also in asteam operation. The conversion is achieved in a short period of timeand without danger This is achieved by lowering the temperature in thecooking space temperature to approximately 100° C. with a spray of waterdirected onto a cooking space wall prior to commencement of the steamoperation.

I claim:
 1. An apparatus for circulated hot air and steam foodtreatment, comprising:a walled housing defining a cooking space; meansfor supplying heated air in said cooking space with a predeterminedtemperature for heated air treatment of a foodstuff in said space; meansfor spraying cold water onto a wall of said housing to cool the same andgenerate water vapor in said cooking space; at least one blower locatednear said wall to be sprayed with said cold water for selectivelycirculating said heated air and water vapor in said cooking space; meansexternal of said generating steam and having a boiler located outsidesaid cooking space, said boiler being connectable to said cooking spacefor a steam food treatment; and control means converting heated airtreatment to said steam treatment for deenergizing said means forsupplying the heated air after said predetermined temperature has beenreached, turning on said means for spraying said cold water until atemperature of about 100° C. has been reached, subsequent closing saidspraying means when the temperature of about 100° C. has been reached,switching on said means for generating said steam while controlling thesteam treatment in said cooking space, and continuously controlling thedesired degree of the temperature in said cooking space for the foodtreatment by said steam.
 2. The apparatus defined in claim 1 whereinsaid spraying means are nozzles.
 3. The apparatus defined in claim 1,further comprising:a selector switch having three positions "off","steam" and "hot air"; an oven thermostat controlling a temperatureduring "hot air" position, a steam thermostat controlling saidconstitution of said steam during the "steam positon", a solenoid steamvalve, said steam valve, being controlled by said steam thermostatduring the "steam position" interrupts the supply of said water vapor,and cooling means havinga wall thermostat controlling the temperature insaid cooking space, and a solenoid water valve interrupting the supplyif said cold water after said temperature about 100° has been reached.